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Life-cycle modification in open oceans accounts for genome variability in a cosmopolitan phytoplankton

06/01/2015

The ISME Journal

9
pp. 1365-1377

Type

Article dans des revues

Authors

Von Dassow Peter

John Uwe

Ogata Hiroyuki

Probert Ian

Bendif El Mahdi

Kegel Jessica

Audic Stéphane

Wincker Patrick

Da Silva Corinne

Claverie Jean-Michel

Doney Scott

Glover David

Mella Flores Daniella

Herrera Yeritza

Lescot Magali

Garet-Delmas Marie-José

De Vargas Colomban

Emiliania huxleyi is the most abundant calcifying plankton in modern oceans with substantial intraspecific genome variability and a biphasic life cycle involving sexual alternation between calcified 2N and flagellated 1N cells. We show that high genome content variability in Emiliania relates to erosion of 1N-specific genes and loss of the ability to form flagellated cells. Analysis of 185 E. huxleyi strains isolated from world oceans suggests that loss of flagella occurred independently in lineages inhabiting oligotrophic open oceans over short evolutionary timescales. This environmentally linked physiogenomic change suggests life cycling is not advantageous in very large/diluted populations experiencing low biotic pressure and low ecological variability. Gene loss did not appear to reflect pressure for genome streamlining in oligotrophic oceans as previously observed in picoplankton. Life-cycle modifications might be common in plankton and cause major functional variability to be hidden from traditional taxonomic or molecular markers.